Active isolation module

ABSTRACT

A vibration isolator for isolating a load from a floor. The vibration isolator may have an active isolator assembly that isolates the load in a first direction and a passive isolator assembly that isolates the member in a second direction or directions. The active isolator assembly may include a single actuator that is coaxially aligned with a sensor. The sensor and actuator can be connected to a controller which together provide active isolation of the load. The passive isolator assembly may include a pendulum that is coupled to a dashpot. Providing a system with just one actuator significantly reduces the cost of the vibration isolator with respect to isolators of the prior art.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a vibration isolator that canisolate a load such as a table platform from a surface such as a floorof a building.

[0003] 2. Background Information

[0004] It is sometimes desirable to prevent relative movement betweentwo surfaces. For example, integrated circuit are typically fabricatedon a platform with photolithographic equipment. The location of directedlight used to align and fabricate the integrated circuit must be veryaccurate.

[0005] The table is typically placed on the floor of a clean room. Thefloor may undergo vibrational movement that can be transferred to thetable. The vibration may cause a displacement of the table which reducesthe accuracy of the fabrication process.

[0006] Some tables incorporate vibration isolators to reduce or preventthe floor vibration from being transferred to the table. U.S. Pat. No.5,000,415 issued to Sandercock and assigned to the assignee of thepresent invention, Newport Corp., discloses a vibration isolator thathas an active isolator assembly which actively isolates a load from afloor. The active isolator assembly includes a plurality ofpiezoelectric actuators which can vary the distance between the load andthe floor surface to compensate for movement in the floor. For example,the floor may oscillate so that the floor surface moves toward the loadand away from the load. When the floor moves toward the load thepiezoelectric actuators contract so that the motion of the load relativeto inertial space is reduced compared to that of the floor. Likewise,when the floor moves away from the load the actuators expand.

[0007] The active vibration isolator disclosed in the Sandercock patentincludes a sensor that senses the movement of the floor and circuitry toprovide a control loop to synchronize the contraction/expansion of theactuators with the movement in the floor. Sandercock also discloses theuse of sensors which sense the velocity of the load to provide afeedback loop that is coupled to the feedforward loop.

[0008] The piezoelectric actuators and control loops are capable ofisolating the load for relatively low frequencies. To roll off highfrequencies, Sandercock employs an elastomeric mount that is interposedbetween the load and the actuators. The elastomeric mount has a resonantfrequency that varies with the weight of the load. The variation in theresonant frequency requires a calibration of the system duringinstallation, or a reconfiguration, to compensate for a different weightof the load. It would be desirable to provide an elastomeric mount whichhas a resonant frequency that is relatively constant for a predeterminedrange of load weights.

[0009] U.S. Pat. No. 5,660,255 issued to Schubert et al. discloses avibration isolator which has a number of piezoelectric actuators toisolate a load in a vertical direction and additional piezoelectricactuators to isolate the load in a horizontal plane. The Schubertvibration isolator provides active isolation in both the vertical andhorizontal directions. The piezoelectric actuators are relativelyexpensive. Therefore providing additional horizontal actuators increasesthe cost of assembling the vibration isolator. It would be desirable tohave effective vibration isolators that can provide vertical andhorizontal isolation, and which cost less to produce than isolators ofthe prior art.

[0010] Even with vibration isolation the load may move relative to thefloor in the horizontal plane. It may be desirable to move and adjustthe load to an original reference position. It would therefore bedesirable to provide a docking system which can align and secure theload in a reference position.

[0011] The drive signal which excites the piezoelectric actuator istypically a function of a gain value and a transfer function which areeither stored in a memory device of a controller that controls thesystem, or built into analog electronics that control the system. Thestored transfer function determines the transient response time andbandwidth of the isolator. Vibration isolators of the prior art do notallow the system operator to vary the transfer function and theresultant transient response time and bandwidth of the system. It wouldbe desirable to provide a vibration isolator which allows an operator tovary the transfer function used to determine the drive signal of theactuator.

SUMMARY OF THE INVENTION

[0012] One embodiment of the present invention is a vibration isolatorfor isolating a load from a surface. The vibration isolator may have anactive isolator assembly that isolates the load in a first direction anda passive isolator assembly that isolates the load in a seconddirection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view of an embodiment of a table assemblyof the present invention;

[0014]FIG. 2 is a side view of a foot of the table assembly;

[0015]FIG. 3 is a cross-sectional view of an embodiment of a vibrationisolator of the table assembly;

[0016]FIG. 4 is a cross-sectional view of a damper assembly of thevibration isolator;

[0017]FIG. 5 is a schematic of the isolator;

[0018]FIG. 6 is an electrical schematic of a controller that controlsthe isolator;

[0019]FIG. 7 is a flowchart showing a routine performed by a controllerof the isolator.

DETAILED DESCRIPTION OF THE INVENTION

[0020] One embodiment of the present invention is a vibration isolatorfor isolating a load from a surface. The vibration isolator may have anactive isolator assembly that isolates the load in a first direction anda passive isolator assembly that isolates the load in a seconddirection. The active isolator assembly may include a single actuatorthat is coaxially aligned with a sensor. The sensor and actuator can beconnected to a controller which together provide active isolation of theload. The passive isolator assembly may include a pendulum that iscoupled to a dashpot. Providing a system with just one actuatorsignificantly reduces the cost of the vibration isolator with respect toisolators of the prior art.

[0021] Referring to the drawings more particularly by reference numbers,FIG. 1 shows an embodiment of a table assembly 10 of the presentinvention. The assembly 10 may include a platform 12 that is supportedby a plurality of legs 14. The platform 12 may have a honeycombconstruction and include a plurality of mounting holes 16 which allowitems such as optical mounts to be attached to the table 10. As analternate embodiment, the platform 12 may be constructed from a slab ofgranite.

[0022] The legs 14 may be interconnected by beams 18. The legs 14 extendfrom a plurality of feet 20. The feet 20 are in contact with a surface22 such as a floor of a building structure.

[0023] As shown in FIG. 2, each foot 20 may include a number of cleats24 that extend from a plate 26. The cleats 24 may penetrate a carpet 28and secure the table 10 to the floor. The cleats 24 assist inmechanically connecting the table 10 to a solid floor located beneaththe carpet.

[0024] Referring to FIG. 1, the table assembly 10 may include one ormore vibration isolators 30. The isolators 30 are typically mounted tothe beams 18 of the table 10, or alternatively mounted in the table legs14. The floor may undergo a vibrational movement that creates a varyingdisplacement of the surface 22. The isolators 30 isolate a load such asthe platform 12 from the varying displacements of the surface 22.

[0025] The table assembly 10 may further include a controller 32 whichcontrols the vibration isolators 30. The controller 32 may control allthree isolators 30. Although three isolators 30 are shown and described,it is to be understood that four or any other combination of isolators30 may be employed in the present invention.

[0026]FIG. 3 shows an embodiment of a vibration isolator 30. Theisolator 30 may have an outer housing 32 that is mounted to a mountingsurface such as a beam 18 by fasteners 34. The housing 32 may include alower section 35 that is attached to an upper section 36 by fasteners38. The isolator 30 may include a post 40 that is attached to the lowersection 35 of the housing 32 by a fastener 42. The isolator 30 may alsoinclude a top plate 44 that supports the platform 12. When the tableassembly 10 is transported, the top plate 44 and platform 12 may besecured by a locking plate 46 and fasteners 47 that screw into the plate44 and the housing 32.

[0027] The isolator 30 may include an active isolator assembly 48 and apassive isolator assembly 50 that isolate the top plate 44 from thehousing 32. The active isolator assembly 48 may isolate the plate 44 andplatform 12 in a first vertical direction. The passive isolator assembly50 may isolate the plate 44 and platform 12 in a second horizontaldirection or plane.

[0028] The active isolator assembly 48 may include a piezoelectricactuator 54 that is mounted to the post 40. The piezoelectric actuator54 may receive a drive signal that either increases or decreases theheight of the actuator 54 to isolate the plate 52 and platform 12 in thevertical direction. The piezoelectric actuator 54 may be constructedfrom a plurality of piezoelectric elements which are maintained incompression by a plurality of elastic elements such as bellville springs60. The actuator 54 also includes a push rod 56 connected to thepiezoelectric elements by connecting blocks 58. The springs 60 arecaptured by a nut 62 that is screwed onto the post 40.

[0029] The push rod 56 is attached to a cup 64 which houses a sensor 66.The sensor 66 may be a geophone which provides an electrical outputsignal that is a function of the motion of the actuator push rod 56.

[0030] The isolator 30 may include a filter assembly 70 that is coupledto the active isolator assembly 48 and the passive isolator assembly 50.The filter assembly 70 may include an elastomer 72 that is attached to acoupler plate 74 and a plug 76 which is screwed into the cup 64. Thefilter assembly 70 filters out relatively high frequency vibrationsintroduced to the isolator 30 so that high frequency components are nottransferred from the floor 22 to the plate 44 and platform 12. Thisreduces the requirements for active system bandwidth.

[0031]FIG. 4 shows an embodiment of a filter assembly 70′ which has aresonant frequency that remains relatively constant for a predeterminedrange of forces that may be applied to the assembly 70. The assembly 70′may include a profiled elastomer 72′ that is located within a profiledcavity 78 of the coupler plate 74. The profiles of the elastomer and thecavity are chosen so that, as load increases, the elastomer is pressedagainst the cavity walls, thereby increasing the stiffness which allowsfor relatively constant natural frequency. By way of example, a conicalshaped elastomer and cavity are chosen for the embodiment shown in FIG.4.

[0032] Referring to FIG. 3, the sensor 66 has a center axis that iscoaxial with a center axis of the actuator 54. Additionally, the centeraxes of the sensor 66 and actuator 44 may be coaxial with a center axisof the filter assembly 70. The coaxial relationship between the actuator54 and sensor 66 allow the sensor 66 to sense axial translationalmovement with minimal bending movements.

[0033] The passive isolator assembly 50 may include a plurality ofcables or other tension members 80 that extend along an inner channel 81of a tube 82. The tube 82 is in contact with the top plate 44. Thebottom ends of the cables 80 each have knobs 84 that are captured by anend plate 86. The end plate 86 is attached to the tube 82. The top endof the cables 80 have knobs 88 that are captured by cable plugs 90 whichare screwed into the coupler plate 74. The cables 80 create a pendulumassembly which allows the top plate 44 and tube 80 to translatehorizontally about the post 40.

[0034] The lower housing section 35 may include a reservoir 91 that isfilled with a fluid 92 such as oil. A portion of the tube 82 extendsinto the reservoir 91. The fluid filled reservoir 91 creates a dashpotthat damps horizontal movement of the plate 44.

[0035]FIG. 5 shows a schematic of the active 48 and passive 50 isolatorassemblies. The plate 44 is coupled to the coupler plate 74, sensor 66and actuator 54 by the tube 82 and cables 80. Flexing of the cables 80between the knobs 84 and 88 allows horizontal motion of the passiveisolator assembly 50. The passive isolator assembly 50 allows relativehorizontal movement between the plate 44 and the floor 22 as indicatedby the arrow 94. The passive assembly 50 also damps the movement withthe dashpot reservoir 91.

[0036] The actuator 54 varies in height to compensate for movement ofthe floor 22 in the vertical direction as indicated by the arrow 96. Theactive isolator assembly 48 prevents or reduces movement of the floor 22from being transferred into the plate 44.

[0037] Referring to FIG. 3, during operation of the isolator 30, the topplate 44 and platform 12 may move relative to the floor 22. It may bedesirable to move the top plate 44 and platform 12 back to a referenceposition.

[0038] The isolator 30 may have a docking assembly 100 that moves andsecures the plate 44 and platform 12 to the reference position. Thedocking assembly 100 may include a pin 102 that is inserted into anaperture 104 of the plate 52. Both the pin 102 and the aperture 104 mayhave lead in chamfer surfaces 106 and 108, respectively, which induce amovement of the plate 52 so that a center axis of the aperture 104 isaligned with a center axis of the pin 102. The center axis of the pin102 provides a reference point for the plate 52 and platform 12.

[0039] The pin 102 may include a sleeve 110 that is attached to anoutput shaft 112 of an actuator 114. The actuator 114 may be a linearstepper motor. The actuator 114 is attached to the housing 32. Theactuator 114 can move the pin 102 into and out of the aperture 104.During isolation, the pin 102 is pulled out of the aperture 104 to allowrelative horizontal movement between the plate 44 and the floor 22. Thepin 102 can be moved back into the aperture 104 to align the plate 44and secure the platform 12.

[0040]FIG. 6 shows a schematic of an embodiment of the controller 32that controls the vibration isolators 30. The controller 32 may includea processor 120 that is connected to a memory device 122 by a bus 124.The processor 120 may be a digital signal processor (DSP), the memorydevice may be non-volatile random access memory such as “flash” memory.The processor 120 may perform software routines in accordance withinstructions and data stored in the memory device 122.

[0041] The controller 32 may include an amplifier 128 and an analog todigital (A/D) converter 130 that are connected to the sensor 66 and thebus 124. The sensor 66 generates an output signal that is a function ofthe motion of the actuator push rod 56 shown in FIG. 3. The amplifier128 amplifies, and may integrate and/or filter, the output signal of thesensor 66. The amplified signal is converted into a digital sequence bythe A/D 130 and provided to the processor 120.

[0042] The controller 32 may also include a digital to analog (D/A)converter 132 and an amplifier 134 that are connected to the actuator 54and bus 124. The processor 120 provides digital sequences that areconverted to an analog signal by the D/A 132. The output of the D/A 132is amplified and provided to the actuator 54 shown in FIG. 3, to cause acontraction or expansion of the piezoelectric.

[0043] The stepper motor 114 may also be coupled to the bus 124 by adriver circuit 135. The processor 120 may provide commands to actuatethe motor 114 and move the pin 102 shown in FIG. 3 in and out of theaperture 104. Although not shown, the processor 120 may be connected toA/D converters, D/A converters and amplifiers for each isolator of amultiple isolator table assembly. The control system may have a singleinput single output architecture or a multiple input multiple outputarchitecture between the processor and the isolators.

[0044] The controller 32 may include an input/output (I/O) port 136 thatis connected to the bus 124. A computer 138 can be connected to thecontroller 32 through the I/O port 136 to store or read information inthe memory device 122. By way of example, the processor 120 typicallyprovides output to the actuator 54 in accordance with a software routinethat utilizes a gain value and a transfer function. The gain andtransfer function can be stored in the memory device 122 through the I/Oport 136.

[0045] A number of different transfer functions can be provided on astorage medium such as a floppy or optical disk 140 that is loaded intothe computer 138. The disk 140 may also contain a software routine whichallows the operator to select one transfer function from a list ofdifferent transfer functions. Different transfer functions may be storedin memory 122 and selected by the operator using the computer 138 andthe I/O port 136. Different transfer functions may provide differenttransient response times for the isolators 30. The selected transferfunction is then stored in the memory device 122 through the I/O port136. The software on the disk 140 may also allow the operator to selecta gain value that is used to compute the output signal provided to theactuator 54. The system thus allows the user to select the gain andtransient response time of the isolators 30.

[0046]FIG. 7 shows a flowchart of a routine performed by the processor120. When the system is initially powered up the processor performs aninitialization routine to undock the docking assembly, provide systemidentification and DC offset correction in process block 150. The DCoffset correction may include reading a DC level from the signalgenerated by the sensors. The DC level can be stored and then latersubtracted from the output signals of the sensors during operation tonormalize the signals.

[0047] After initialization, the process continues to process block 152to read the output signals of the sensors. The process then determineswhether to perform a docking routine in block 154. In block 156 thesaturation values are checked and updated.

[0048] The output signals for the actuators are calculated in block 158.The calculations utilize the transfer function and gain value stored inthe memory device. In block 160 the output signals are provided to theD/A converter to actuate the piezoelectric devices. The process thenreturns to block 152 and repeats the routine.

[0049] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various othermodifications may occur to those ordinarily skilled in the art.

What is claimed is:
 1. A vibration isolator which isolates a load thatis separated from a floor, comprising: an active isolator assembly thatprovides active isolation of the load in a first direction; and, apassive isolator assembly that provides passive isolation of the load ina second direction.
 2. The vibration isolator of claim 1, wherein thefirst direction is parallel with a vertical axis and the seconddirection is parallel with a horizontal axis of the load.
 3. Thevibration isolator of claim 1, wherein said passive isolator assemblyincludes a pendulum assembly.
 4. The vibration isolator of claim 3,wherein said pendulum assembly includes a cable that is coupled to theload.
 5. The vibration isolator of claim 4, wherein said passiveisolator assembly includes a dashpot that is coupled to said pendulumassembly and the floor.
 6. The vibration isolator of claim 1, whereinsaid active isolator assembly includes an actuator that is coupled tothe load and the floor.
 7. The vibration isolator of claim 6, whereinsaid active isolator assembly includes a sensor that senses a movementof a point between the load and the housing, and a controller which iscoupled to said actuator and said sensor and which provides a drivesignal to said actuator in response to a feedback signal from saidsensor.
 8. The vibration isolator of claim 7, wherein said drive signalis a function of a transfer function and said transfer function isselectable from a plurality of different transfer functions.
 9. Thevibration isolator of claim 7, wherein said sensor has a center axisthat is coaxial with a center axis of said actuator.
 10. The vibrationisolator of claim 1, further comprising a filter assembly that iscoupled to said active isolator assembly and the load.
 11. The vibrationisolator of claim 10, wherein said filter assembly includes a profiledelastomer that is located within a profiled cavity of a coupler plate,so that a resonant frequency of said filter assembly is essentiallyconstant for a predetermined range of loads applied to said filterassembly.
 12. The vibration isolator of claim 11, wherein said profiledelastomer and profiled cavity each have a conical shape.
 13. Thevibration isolator of claim 1, further comprising a docking assemblythat secures the load relative to the housing.
 14. The vibrationisolator of claim 13, wherein said docking assembly includes a pin thatcan be inserted into an aperture of a plate that supports the load. 15.The vibration isolator of claim 1, further comprising a foot thatsupports said active and passive isolator assemblies and which has acleat that can be embedded into the floor surface.
 16. A method forisolating a load from a floor, comprising: a) actively isolating theload in a first direction; and, b) passively isolating the load in asecond direction.
 17. A vibration isolator which isolates a load that isseparated from a floor, comprising: an actuator that is coupled to theload and the floor, said actuator having a center axis; and, a sensorthat is coupled to said actuator and the load, said sensor having acenter axis that is coaxial with the center axis of said actuator. 18.The vibration isolator of claim 17, further comprising a controllerwhich is coupled to said actuator and said sensor and which provides adrive signal to said actuator in response to a feedback signal from saidsensor.
 19. The vibration isolator of claim 18, wherein said drivesignal is a function of a transfer function and said transfer functionis selectable from a plurality of different transfer functions.
 20. Thevibration isolator of claim 17, further comprising a filter assemblythat is coupled to said sensor and the load.
 21. The vibration isolatorof claim 20, wherein said filter assembly includes a profiled elastomerthat is located within a profiled cavity of a coupler plate, so that aresonant frequency of said filter assembly is essentially constant for apredetermined range of loads applied to said filter assembly.
 22. Thevibration isolator of claim 21, wherein said profiled elastomer andprofiled cavity each have a conical shape.
 23. The vibration isolator ofclaim 17, further comprising a docking assembly that secures the loadrelative to the floor.
 24. The vibration isolator of claim 23, whereinsaid docking assembly includes a pin that can be inserted into anaperture of a plate that supports the load.
 25. A vibration isolatorwhich isolates a load that is separated from a floor, comprising: anactive isolator assembly that provides active isolation of the load;and, a docking assembly that secures the load relative to the floor. 26.The vibration isolator of claim 25, wherein said docking assemblyincludes a pin that can be inserted into an aperture of a plate thatsupports the load.
 27. The vibration isolator of claim 26, wherein saiddocking assembly includes a stepper motor which moves said pin into saidaperture.
 28. The vibration isolator of claim 26, wherein said activeisolator assembly includes an actuator that is coupled to the load andthe floor, a sensor that senses a movement of a point between the loadand the floor, and a controller which is coupled to said actuator andsaid sensor and which provides a drive signal to said actuator inresponse to a feedback signal from said sensor.
 29. The vibrationisolator of claim 28, wherein said drive signal is a function of atransfer function and said transfer function is selectable from aplurality of different transfer functions.
 30. The vibration isolator ofclaim 28, wherein said sensor has a center axis that is coaxial with acenter axis of said actuator.
 31. A method for isolating and securing aload to a floor, comprising: a) actively isolating the load from thefloor; and, b) activating a pin which couples and secures the load tothe floor.
 32. The method as recited in claim 31, wherein the pin ininserted into an aperture of a plate that supports the load.
 33. Avibration isolator which isolates a load that is separated from a floor,comprising: an actuator that is coupled to the load and the floor; asensor that senses a movement of a point between the load and the floor;and a controller which is coupled to said actuator and said sensor andwhich provides a drive signal to said actuator in response to a feedbacksignal from said sensor, said drive signal being a function of atransfer function that is selectable from a plurality of differenttransfer functions.
 34. The vibration isolator of claim 33, furthercomprising a passive isolator assembly that passively isolates the load.35. The vibration isolator of claim 34, wherein said passive isolatorassembly includes a pendulum assembly.
 36. The vibration isolator ofclaim 35, wherein said pendulum assembly includes a cable that iscoupled to the load.
 37. The vibration isolator of claim 35, whereinsaid passive isolator assembly includes a dashpot that is coupled tosaid pendulum assembly and the floor.
 38. The vibration isolator ofclaim 33, wherein said sensor has a center axis that is coaxial with acenter axis of said actuator.
 39. The vibration isolator of claim 33,further comprising a damper assembly that is coupled to said sensor andthe load.
 40. The vibration isolator of claim 39, wherein said filterassembly includes a profiled elastomer that is located within a profiledcavity of a coupler plate, so that a resonant frequency of said filterassembly is essentially constant for a predetermined range of loadsapplied to said filter assembly.
 41. The vibration isolator of claim 40,wherein said profiled elastomer and profiled cavity each have a conicalshape.
 42. The vibration isolator of claim 33, further comprising adocking assembly that secures the load relative to the floor.
 43. Thevibration isolator of claim 42, wherein said docking assembly includes apin that can be inserted into an aperture of a plate that supports theload.
 44. The vibration isolator of claim 39, further comprising a footthat supports said actuator and said sensor and which has a cleat thatcan be embedded into the floor.
 45. A method for isolating a load from afloor, comprising: a) selecting a transfer function from a plurality ofdifferent transfer functions; b) sensing a motion between the load andan inertial reference; and c) driving an actuator with a drive signalthat is a function of the selected transfer function.
 46. The method ofclaim 45, wherein the transfer function is selected by storing thetransfer function in a memory device.
 47. A foot for a vibrationisolator that isolates a load from a floor, comprising: a plate; and, acleat that extends from said plate and can be embedded into the floor.41. A vibration isolator which isolates a load that is separated from afloor, comprising: an active isolator assembly that provides activeisolation of the load; and, a plate that is coupled to said activeisolator assembly; and, a cleat that extends from said plate and can beembedded into the floor.
 49. The vibration isolator of claim 48, furthercomprising a passive isolator assembly that provides passive isolationof the load.